Health officials in China examine a pigeon for H7N9 virus at a poultry market in Changsha, Hunan province in April. Researchers in the U.S. are now testing a vaccine that, if needed, could help combat the spread of the deadly bird flu strain. (Photo: Reuters/China Daily)

A bird flu vaccine to combat the deadly H7N9 virus in China is in its next stage of development: Clinical testing.

The virus, which the World Health Organization calls one of the most lethal flu viruses in the world, causes severe pneumonia, among other symptoms of fever, cough and shortness of breath.

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In late March, a new strain of bird flu that adapted in a way that allowed the virus to thrive in human hosts surfaced in China. The first recorded case of the H7N9 virus was reported on March 31. As of May 13, the death toll from the new strain of bird flu virus has reached 35 people, and the number of infections is at 130, according to Reuters.

Avian flu viruses are a group of influenza viruses that usually infect birds. Many strains of the virus cannot survive in humans; but the H7N9 strain has adapted to thrive in human cells. IScience Times reported earlier that researchers at the Influenza Virus Research Center in Tokyo found that the H7N9 had mutated in a way that allows it to spawn in temperatures similar to those of the upper respiratory tract of humans.

Live Science reports that researchers at the U.S. Centers for Disease Control and Prevention, or CDC, have already put together a vaccine against the bird flu virus. Not wanting to lose valuable time, the CDC manufactured its own vaccine in early April instead of waiting for a sample to be shipped from China.

And now, it's time to begin testing. Volunteers in the U.S. will be pulled together for a trial, during which health personnel will monitor the volunteers' reactions to the vaccine and determine the vaccine's safety.

Still, it's not certain that the vaccine is even necessary, given that the virus seems to have been relatively contained. From Live Science:

Health officials are not yet sure whether they will need to use the H7N9 vaccine. The decision to produce large quantities of the vaccine and vaccinate the public will depend on whether H7N9 turns into a global disease outbreak, Faucisaid.

Right now, cases of H7N9 have not been seen outside China and Taiwan, and there have been no reports of sustained human-to-human transmission of the virus.

The virus' spread seems to be slowing down, following a number of containment efforts like chicken and pigeon vaccination, mass chicken incineration and quarantining of infected humans.

The deadly virus outbreak has left an indelible mark on China's poultry market, however. Reuters reports that demand for poultry products in China has plummeted. China's chain of 5,300 KFC restaurants, under the parent company Yum Brands Inc, took a nose dive, and reported a 30 percent drop in sales for April. From Reuters:

The bird flu outbreak has hobbled the company's effort to revive sales in China, where restaurant sales tumbled after a highly publicized report in mid-December highlighted excessive levels of antibiotics in chicken from two of Yum's suppliers. Yum was not fined by food safety authorities, but it suffered a widespread backlash in the mainstream media and on Weibo, the China equivalent of popular U.S. social media site Twitter.